This invention relates to a retroreflector which may be used wherever light reflection is desired. A leading application of the retroreflector is as a marking tape for roadways, pavements, airport runways, vertically disposed signs and the like, and therefore it is described with respect to these uses.
Retroreflective tapes or strips are mounted on the surface of a roadway, such as along its center line or shoulders, to delineate paths or lanes for traffic, or at intersections to define stopping lines or cross-lanes for traffic, both vehicular and pedestrian. Markers of this type are mounted in spaced apart relation and serve to guide traffic in following or traversing a roadway, or in following a curve or grade in the roadway. Particularly to assist a driver of a vehicle at night, these markers have light reflectors which catch and return incident beams of light from vehicular headlights back toward the source of the light. Since automobiles of recent vintage have quite powerful headlights, the use of marking tapes has become more widespread. Marking tapes contribute to traffic safety such as when roads are wet from rain. Under certain conditions, such as fog, light-reflecting road marking means can be the only way of orienting a driver to a changing direction of a road.
Several forms of retroreflective marking tapes have been suggested. They suffer from one or more limitations, such as reflecting too small a proportion of incident light while an approaching vehicle is still at an appreciable distance; or being susceptible excessively to exposure to the weather, particularly rain alone or with subsequent freezing. The practice has been to place light-reflecting elements at or even above the upper level of the road marking tape. But at this location, the light-reflecting units are not only subject to wear and even breakage from vehicular and foot traffic, but as well to erosion and the damaging effects due to entry of water and the like. Further, the accuracy and intensity of light-reflection of such marking tapes are often adversely affected when wet by rain.
For example, in U.S. Pat. No. 3,587,415 to Eigenmann a marking tape is disclosed having a plurality of spaced elements arranged on and partly embedded in the top of a base strip, the elements being of a composition having a substantial amount of microspheroids to provide light reflection.
U.S. Pat. No. 3,920,346 to Wyckoff discloses a marker strip provided with spaced wedges having embedded centrally therein an upwardly oriented retroreflective material, such as glass beads, in right-angled position with respect to a roadway. In such a construction, there is no effort to orient refracted light with the retroreflective material so as to obtain maximum reflectivity. Even more serious, should a wedge become broken for any reason, water and like debris have easy entry and access to the retroreflective material to destroy its effectiveness.
U.S. Pat. Nos. 3,935,365 to Eigenmann discloses a tape material having a twin-layer structure including a lower relatively thin support layer and an upper principal thicker layer formed of a composition having hard crystalline particles and light-reflecting particles embedded therein at various levels.